The present invention relates to a sub frame structure of a vehicle in which a rear suspension of the vehicle is supported, for example.
In a vehicle, such as an automotive vehicle, a rear suspension connecting a rear wheel and a vehicle body performs a function of pressing the rear wheel against a road surface and another function of a shock absorber to suppress an impact of unevenness of the road surface on the vehicle body. There are various types of rear suspension performing these functions in a suspension mechanism and the like.
Japanese Patent Laid-Open Publication No. 2013-169812, for example, discloses a multi-link type of rear suspension, in which plural arm members are connected to a rear sub frame, the rear sub frame being formed in a parallel crossed shape by a pair of right-and-left side members and front-and-rear cross members which are spaced apart from each other in a vehicle longitudinal direction and interconnect the side members, respectively.
More specifically, the multi-link type of rear suspension disclosed in the above-described patent document is configured such that a front-side lower arm, a rear-side lower arm, and an upper arm, which are respectively coupled to a rear wheel via a knuckle, are connected to the rear sub frame, and a trailing arm, a front end of which is connected to a vehicle body, is connected to the knuckle.
Herein, in the multi-link type of rear suspension like the one disclosed in the above-described patent document, when an input caused by the unevenness of the road surface or the like acts on the rear wheel from a front side of a vehicle, a load is applied to the rear suspension obliquely upward and rearward.
Herein, a vertical load (load acting in a vertical direction) which is part of the above-described upward-and-rearward oblique load is absorbed by a swinging movement of the arm members, such as the front-side lower arm, and a biasing force of a suspension spring. Meanwhile, a longitudinal load (load acting in the vehicle longitudinal direction) is transmitted to the rear sub frame through the front-side lower arm and the rear-side lower arm and also transmitted to the vehicle body through the trailing arm.
Therefore, in a case in which the trailing arm of the above-described multi-link type of rear suspension of the patent document is omitted, for example, the longitudinal load transmitted to the rear sub frame through the front-side lower arm and the rear-side lower arm may increase.
In this case in which the longitudinal load transmitted to the rear sub frame increases, it is necessary to improve the strength of the side member against the longitudinal load. However, if the side member's strength is improved, there is a problem that the side member may not serve as a collision-load absorbing member properly in a vehicle rear collision.